Display screen or portion thereof with transitional graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with transitional graphical user interface showing a first screen of a series in accordance with our new design;

FIG. 2 is a second image thereof; and,

FIG. 3 is a third image thereof.

The broken lines showing a portion of a display screen forms no part of the claimed design.

The appearance of the graphical user interface sequentially transitions between the images shown in FIGS. 1-3. The process or period in which one image transitions to another image forms no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with transitional graphical user interface, substantially as shown and described. 